Estimating packaged software committee

Package implementations often fail...can't they be estimated accurately?

Assignment:

To develop a clear methodology to size and to estimate COTS/ERP package implementations. These include standard software package like SAP, Oracle EBS and Siebel. Starting point is that there is standard functionality that has to be configured to match the organizational processes. Almost always, the software package does not support all of the organization processes and some custom-made software has to be developed. A typical COTS/ERP package implementation can be divided into three main parts: